97 Nissan Quest overheating.

My friend has a 97 Nissan Quest that he bought used. He told me that the blower fan will kick not kick into it’s third position, after the vehicle has been running a few minutes, and that it causes overheating. Now, the funny thing is, if he turns on the AC, the fan kicks in, and theradiator temp goes down.
So, question: What causes the fan to not turn on at any other time, and do so at this time?
How much should it cost to fix?

Oh, btw, it had been in a wreck, and he says that the electrical system was damaged! Now, he tells me.


Hoo boy. Let’s try to clear this up.

The blower is a fan in the heat/vent/AC ductwork, controlled by the driver with a switch. An inoperative blower will not cause overheating. If the blower doesn’t work in 3rd speed, the driver can simply switch to 2nd or 4th speed to still have blower operation.

The radiator fan is in the engine compartment immediately next to the radiator. It comes on as needed, when the engine temperature reaches a certain point. In many vehicles, it also comes on when the AC high-side pressure reaches a certain point, or when the AC is switched on. Presumably on this vehicle it’s the latter.

So it sounds like the radiator fan fails to switch on by engine temperature, but does switch on by AC engagement. This gives the driver a chance to alleviate the symptom caused by a problem in the radiator fan control circuit. The cost to find and fix that problem can vary over a wide range depending on the particular cause. I don’t have enough info here to narrow it down to one most likely thing.

Note that the radiator fan is only needed when going slowly or sitting still. At higher road speeds, airflow through the radiator makes the fan superfluous.

I’ve had to make some assumptions based on what I think the OP is trying to describe – as written it’s largely nonsensical. Blower fans have a 3rd position, but their failure will NOT cause overheating. Radiator fan failure can cause overheating, but they do NOT have a “3rd position.” Blower speeds are directly selected by the driver, they don’t “kick in.” Radiator fans kick on, but what the heck is this “3rd position” he’s talking about? No vehicle will overheat, fan working or not, only a few minutes after a cold start.

“Electrical system” covers a lot of ground. There’s electrical stuff throughout the engine and the vehicle as a whole, and I’m sure it wasn’t all damaged. Knowing EXACTLY what was damaged might be helpful in determining whether it could or could not relate to the fan situation.